1. Field of the Invention
The invention relates generally to computer systems and more specifically to hard disk drives with miniature disks of high storage capacity, e.g., one and eight tenths inch (1.8") diameter disks that store at least forty megabytes (40 MB).
2. Description of the Prior Art
Huge numeric computer systems constructed during World War II were used to crack secret German military codes. With the advance of technology, the same computing power can now be placed in a handheld computer that sells at commodity prices. The advances in electronics and semiconductor technology that made this possible brought business computing to a personal level, e.g., in the IBM PC, Apple Macintosh, and other personal computer systems. Recently, personal computing has seen the introduction of the battery-powered portable computer, the so-called laptop computer, the still smaller notebook computer, and even a palmtop computer that is so small that it fits in a person's hand.
While computers have been getting smaller in physical size, their memory and execution speeds have grown. To illustrate, one of the first operating systems for personal computers was called CP/M and marketed by Digital Research of Garden Grove, CA. The CP/M operating system ran on 64K bytes of main memory and used only one or two 250K byte eight-inch floppy disk drives. Today, certain laptop computer models, e.g., one by Apple Computer, Inc., require four megabytes of main memory and forty megabytes of built-in hard disk storage just to comfortably run Macintosh System-7 software system and a professional wordprocessor, e.g., Microsoft WORD.
As a result of progressive innovation, hard and floppy disk drives have been migrating to smaller diameter disks. In 1980, the eight-inch hard disk standard drive was popular. More storage was later offered in the five-and-a-quarter-inch (5.25") mini-drives. And subsequently, new demands for still smaller disk drives produced the three-and-a-half-inch (3.5") standard drive.
A typical micro-Winchester 3.5 inch drive is described in U.S. Pat. No. 4,568,988, issued Feb. 4, 1986, to McGinlay, et al. This micro-Winchester was developed to provide the storage capacity and interface of a 5.25" mini-drive. This was possible because track densities of six hundred tracks per inch (TPI) were not a problem to the more advanced head positioning servo systems using voice coil motors (VCM) instead of stepper motor positioning. Specially plated hard disk media were required by micro-Winchester drives, so an industry of disk media suppliers evolved that offered 3.5 inch media as a standard inventory item. This prompted scores of other disk drive manufacturers to also base designs on the 3.5 inch format.
The disk drive and media industry then settled on a two-and-a-half-inch (2.5") size for still further advances in micro miniaturization. This form factor allows a drive that has a length equal to the width of a 3.5 inch drive and a width one-half the length of a 3.5 inch drive. In other words, two 2.5 inch drives are capable of fitting within the space that a 3.5 inch drive typically requires. Drives of such size can be directly secured to printed circuit boards (PCBs), as opposed to the traditional panel and chassis mounting of standard sized drives. For example, the Apple Macintosh Powerbook 140 model 4/40, a laptop personal computer, uses a 2.5 inch forty megabyte hard disk drive similar to that described in U.S. Pat. No. 5,025,335, issued Jun. 18, 1991, to Stefansky. Closed-loop, embedded servo positioning systems are used, as well as head parking mechanisms to avoid having the heads slap against the data media areas while the laptop computer is being carried around and transported. Stefansky realized that further reductions in the size of disk drives would not be possible without redesigning certain components of the reduced size drive. The challenge in such invention lies in the reduction to practice, and not in the conception of a still smaller disk format. As Stefansky points out, the standard flexure used to mount heads on a load beam had to be changed to fit the smaller drives.
A one-and-eight-tenths-inch (1.8") hard disk drive recently became available. For example, Integral Peripherals, Inc. (Boulder, Colorado) markets two models, a twenty megabyte (20 MB) MUSTANG 1820 and a forty megabyte (40 MB) STINGRAY 1842. The forty megabyte storage capacity model incorporates a dual platter 1.8 inch design. Published datasheets comment that the MUSTANG 1820 and STINGRAY 1842 models are designed for use in subnotebook, pen-based and palmtop computers. The 1.8 inch format is purported to be one half the size and weight of 2.5 inch drives. A ramp head loading device PG,5 allows the drive to be spun down to remove the heads from harms way. A lock keeps the heads parked in a safe place. The stated advantage of this is that the drive spins up to speed in less than one second with the heads parked. The following Table I summarizes the specifications for the MUSTANG 1820 and STINGRAY 1842 as published by Integral Peripherals, Inc.
TABLE I ______________________________________ MUSTANG STINGRAY ______________________________________ Formatted Per Drive 21.4 MB 42.5 MB Capacity Per Track 8704 Bytes 8704 Bytes Per Sector 512 Bytes 512 Bytes Sectors Per Track 17 17 Functional Recording 46,100 46,100 Density (BPI) Flux Density 34,600 34,500 (FCI) Area Density 89.5 89.5 (MB/sq in) Disks 1 2 Data Heads 2(4) 4(5) Data Cylinders 615 977 Track Density 1942 1942 (TPI) Recording 1,7 RLL Code 1,7 RLL Code Method Per- Media transfer 1.13 to 1.79 1.13 to 1.79 formance Rate MB/sec MB/sec Interface Transfer Up to 4.0 Up to 4.0 Rate MB/sec MB/sec Rotational Speed 3,571 RPM 3,571 RPM Latency 8.5 ms 8.5 ms Average Seek &lt;20 ms &lt;21 ms Time Track to Track 8 ms 8 ms Seek Time Maximum Seek 30 ms 30 ms Time Start Time 1.5 sec 1.5 sec (Typical) Buffer Size 32K bytes 32K bytes Interface AT/XT AT/XT Relia- MTBF 100,000 hours 100,000 hours bility Start/Stops 1,000,000 1,000,000 Unrecoverable &lt; 1 per 10.sup.13 &lt;1 per 10.sup.13 Data bits read bits read Error Rate Power 5 VDC .+-. 0.8 Amps 0.8 Amps 5%' Startup Current Typical Power Dissipation Spin-up 3.5 watts 3.8 watts Idle 1.0 watts 1.1 watts Read/Write/Seek 2.0 watts 2.1 watts Power Savings 0.5 watts 0.6 watts Mode Standby Mode 0.035 watts 0.035 watts Sleep Mode 0.015 watts 0.015 watts Environ- Temperature mental Operating 5.degree. C. to 55.degree. C. 5.degree. C. to 55.degree. C. Non-operating -40.degree. C. to -40.degree. C. to 70.degree. C. 70.degree. C. Relative Humidity 10% to 90% 10% to 90% (RH) non-condensing non-condensing Maximum Wet 30.degree. C. 30.degree. C. Bulb Shock (11 ms) Operating 10 G 10 G Non-operating 200 G 200 G Vibration (0 to peak) Operating 2 G 2 G Non-operating 10 G 10 G Altitude Operating -1,000 to -1,000 to 10,000 feet 10,000 feet Non-operating 40,000 feet 40,000 feet (maximum) Physical Stacked 15 mm .times. 51 15 mm .times. 51 Configuration (HDA & PCB) mm .times. 77 mm mm .times. 77 mm Low Profile Configuration: Head Disk 10 mm .times. 51 12 mm .times. 51 Assembly (HDA) mm .times. 70 mm mm .times. 70 mm Electronics Card 7 mm .times. 51 7 mm .times. 51 (PCBA) mm .times. 77 mm mm .times. 77 mm Weight &lt;95 grams &lt;95 grams ______________________________________
The ramp assembly in the Integral Peripheral drives confiscates the outermost diameter of the disk platters. In other designs, the passive latch design allows a magnetic bias that is too strong to permit data recording on the innermost data tracks. These areas are therefore not available for data recording, and severely limit storage capacity.